In order to light a cold cathode fluorescent discharge tube used as a backlighting light source for liquid crystal, for example, an H-shaped bridge circuit 80 shown in FIG. 8 is used.
The H-shaped bridge circuit 80 comprises a first transistor 81 and third transistor 83 at a high side, and a second transistor 82 and fourth transistor 84 at a low side. A load 86 such as, for example, a cold cathode fluorescent discharge tube, etc. is connected between a connection node A1 between the emitter electrode of the first transistor 81 and the collector electrode of the second transistor 82, and a connection node A2 between the emitter of the third transistor 83 and the collector of the fourth transistor 84.
When a control circuit 85 switches on or off the first transistor 81 and fourth transistor 84, and the second transistor 82 and third transistor 83 alternately in the H-shaped bridge circuit 80, a current flows across the connection node A1 and the connection node A2 alternately, thereby enabling the load 86 to operate. In this manner, a direct-current voltage is converted into an alternating current in the H-shaped bridge circuit 80, making it possible to light, for example, a cold cathode fluorescent discharge tube.
In a case where such an H-shaped bridge circuit 80 is constructed on a single semiconductor device, four transistors and a control circuit for controlling them are mounted on a substrate. Therefore, the planar area of the semiconductor device becomes large, giving rise to a problem that the size of the semiconductor device becomes large.
Hence, such a method can be considered which reduces the planar area of the semiconductor device by stacking semiconductor elements, as disclosed in, for example, Unexamined Japanese Patent Application KOKAI Publication No. S55-111151.